Communications systems that are reliant upon Orthogonal Frequency Division Multiplexing schemes, for example Long Term Evolution (LTE) communications systems, which are sometimes referred to as 4G communications systems, are known to employ base stations, sometimes referred to as evolved Node Bs (eNode Bs) capable of communicating with User Equipment (UE) units. The UE units are typically used by subscribers to one or more cellular communications services provided by a network infrastructure that comprises a plurality of the eNode Bs to support a respective plurality of notional cells that provide wireless communications coverage for the UEs over a geographic region. The eNode Bs and the UE units are examples of communications equipment that comprise modems. For some applications, it is desirable to implement a modem using a baseband Integrated Circuit (IC) operably coupled to a separate Radio Frequency (RF) IC, because greater design flexibility is achieved.
In the UE unit, the baseband IC and the RF IC together support a transceiver architecture having a transmit chain and a receive chain that support operation in accordance with the different variants of the Orthogonal Frequency Division Multiplexing (OFDM) communications scheme used respectively for uplink and downlink communications. Typically, a received signal is down-converted by the RF IC and communicated to the baseband IC centred about a frequency in a range of baseband frequencies. Similarly, digital signals to be transmitted are generated in the baseband IC, centred about a frequency in the range of baseband frequencies, and communicated to the RF IC, where they are modulated onto a carrier signal having a carrier frequency. The signals communicated between the baseband IC and the RF IC are communicated via a digital interface.
However, LTE and, especially the LTE-Advanced variant, employs a number of methods to increase wireless communications data rate and/or reliability, for example Multiple Input Multiple Output (MIMO) and carrier aggregation. Such optimisations result in an increase in the amount of data that the digital interface needs to support being communicated thereacross. Increasing data throughput with respect to the digital interface introduces undesirable consequences, for example, an increase in power consumption attributable to the digital interface and an increase in the complexity of the digital interface, such as by virtue of a requirement to increase the number of physical pins to support data communication between the broadband IC and the RF IC. Indeed, the design of the digital interface has been continually optimised in order to support progressively more stringent bandwidth requirements, energy consumption requirements and attempts to minimise signal interference between ICs. However, as indicated above, certain optimisations are accompanied by an associated technical cost, which sometimes also has negative financial implications.
US patent publication no. 2013/3315288 also strives to reduce the amount of data transmitted over a digital interface. However, the saving in data throughput is achieved by controlling word length of digital samples of a received signal.